The present invention relates to a loudspeaker apparatus used for a variety of acoustic devices, video devices and the like, particularly to a loudspeaker apparatus in which the strength of a junctional flat portion of an acoustic diaphragm has been improved.
As an acoustic diaphragm used for a loudspeaker apparatus in related art, there is an acoustic diaphragm 10 shown in FIG. 1, for example. FIG. 1 shows a construction which has been cut in half for an explanation. The acoustic diaphragm 10 includes a domed diaphragm 11 shaped like a dome in the center, and an edge-like diaphragm 12, which is formed of a macromolecular film, metal or the like, and is integrally formed in such a manner as to have a predetermined curvature of concavity or convexity or to be linear in cross section from the circular edge of this domed diaphragm 11. Further, a diaphragm edge 14 is integrally formed so as to be connected to the outer circumferential portion of the edge-like diaphragm 12 through a junctional flat portion 13.
A bobbin 16 on which a voice coil 17 is wound is joined to the junction of the acoustic diaphragm 10, where the domed diaphragm 11 and the edge-like diaphragm 12 are combined to a single unit, in such a manner as to hang down, and the voice coil 17 is disposed inside a gap forming magnetic space not shown in the figure to oscillate up and down, and thus a loudspeaker apparatus is assembled. Adhesive is used for joining the acoustic diaphragm 10 and the bobbin 16 together.
A loudspeaker apparatus using this acoustic diaphragm shown in FIG. 1 is constructed, for example, as a dynamic loudspeaker which is relatively small and is capable of reproducing up to a high frequency (for example 100 kHz). Since this kind of acoustic diaphragm 10 has been obtained by integrally molding a thin metal sheet of, for example, aluminum, titanium, or a macromolecular sheet or the like, there has been an inconvenience that the metal sheet and macromolecular sheet at the portion where the domed diaphragm 11 and the edge-like diaphragm 12 are joined together becomes thin due to being stretched in both the directions of the domed diaphragm 11 and the edge-like diaphragm 12 when shaped into a diaphragm, with the result that mechanical strength of the joined portion decreases.
Also, if the bobbin 16 is stuck to the junction between the domed diaphragm 11 and the edge-like diaphragm 12, and an acoustic signal is input to the voice coil 17, a predetermined frequency will cause the vibrations of the domed diaphragm 11 and the edge-like diaphragm 12, whose phases are different by 180 degrees, with the thin, mechanically weak junctional flat portion 13 being a node. With this frequency, there has been an inconvenience in which an acoustic signal emitted from the domed diaphragm 11 and an acoustic signal emitted from the edge-like diaphragm 12 are mutually cancelled, causing a dip in acoustic pressure. Particularly, if this dip is in the audible band, there has been an inconvenience in which the quality of acoustic signals is lowered.
Further, on high frequencies of 20 kHz or more, driving force from the bobbin 16 is absorbed by adhesive and the adhesive surface of the mechanically weak diaphragm 10, and so the driving force is not transmitted to the edge-like diaphragm 12. Thus, a problem in which the necessary acoustic pressure may not be obtained on high frequencies of 20 kHz or more remains to be solved.
As shown in FIG. 2, in order to solve the above problems, the inventor of the present invention and others previously proposed in Japanese Published Patent Application No. 2003-348691 a construction in which a reinforcement ring 15 made of a resinous film is attached to the adhesive point of a bobbin 16 of an acoustic diaphragm 10, and so the bobbin 16 can be installed through the reinforcement ring 15. By thus attaching a bobbin to an acoustic diaphragm through a reinforcement ring, the mechanical strength of the relevant part increases, thereby solving the above-mentioned problems.
There will be no problem arising if the above-mentioned reinforcement ring is made into a shape in advance which is suitable to be stuck and fixed, and then it is stuck and fixed using adhesive, after a loudspeaker diaphragm formed by joining a domed diaphragm and an edge-like diaphragm has been molded. However, if a reinforcement ring is stuck and fixed when a loudspeaker diaphragm is formed by joining a domed diaphragm and an edge-like diaphragm to be molded, the following problems will arise.
Specifically, if molding is executed in accordance with press molding, pneumatic molding, vacuum molding or a molding method combining those, using an extremely impermeable resinous film such as polyethylene terephthalate, polyethylene naphthalate, polyimide, polyetherimide or polycarbonate, an extremely impermeable metal film such as aluminum or titanium or other impermeable film as the material for a loudspeaker diaphragm, through-holes of some kind are provided or a porous mold is used to allow air existing between a film and a diaphragm-molding mold to escape. If a reinforcement ring is stuck and fixed using those extremely impermeable materials, when molding a diaphragm, by means of a diaphragm-molding method, it is necessary to allow air existing between the diaphragm and the reinforcement ring to escape by some means. If a reinforcement ring is made of, for example, the above-mentioned resinous film, it is relatively easy to shape the resinous film into a reinforcement ring, but air is left between a diaphragm and the reinforcement ring when the diaphragm is molded, so that there is a problem that the diaphragm and the reinforcement ring are not firmly stuck to each other.
If air is left between a diaphragm and a reinforcement ring in this manner, adhesive strength between the reinforcement ring and the diaphragm decreases to the extent, eventually causing a problem in which the above-mentioned insufficient mechanical strength of a diaphragm may not be solved.
The present invention is designed in light of the above, and aims to provide a loudspeaker apparatus in which a diaphragm of a loudspeaker apparatus is reinforced easily and favorably.